JP5751528B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus including an optical scanning device that scans a photosensitive member with light.

  In recent years, electrophotographic image forming apparatuses used in laser printers, laser plotters, digital copiers, laser facsimiles, or multi-function machines including these have become more colorized and faster, and photoconductor drums that are image carriers. Tandem type image forming apparatuses having a plurality of (usually four) are widely used.

  Then, it has been devised that the light beam is obliquely incident on the deflecting reflection surface of the optical deflector to reduce the cost (for example, see Patent Document 1 and Patent Document 2).

  However, an image forming apparatus using an optical scanning device having a scanning optical system disclosed in Patent Document 1 and an image forming apparatus using an optical scanning device disclosed in Patent Document 2 are manufactured on a photosensitive drum. If there is an error or an assembly error, there is a possibility that the scanning line bending or the scanning line inclination fluctuates. Note that manufacturing errors of the photosensitive drum include a non-circular cross-sectional shape, non-uniform outer diameter, and eccentricity. Further, assembling errors of the photosensitive drum include deviation of the assembling position from the designed position, inclination in the axial direction with respect to the designed main scanning direction, and the like.

The present invention relates to an image forming apparatus including a photosensitive member and an optical scanning device that optically scans a scanning region of the photosensitive member along a first direction. The optical scanning device emits a light source and the light source. An optical deflector that deflects the light beam incident obliquely with respect to a second direction orthogonal to the first direction, and a scanning optical system that guides the light beam deflected by the optical deflector to the photoconductor. Have
With respect to the incident angle of the light beam that scans within the scanning region, the absolute value of the incident angle of the light beam that is incident on the central portion in the first direction of the scanning region is at both ends of the scanning region in the first direction. much larger than the absolute value of the angle of incidence of the light beam incident with respect to said first direction, a central portion of the scanning region 0, the one end of the scanning region -Ymax, and Ymax other end Using the coordinates, the absolute value | Yp | of the incident position where the incident angle becomes 0 ° with respect to the first direction satisfies the relationship of 0.8 × | Ymax | <| Yp | ≦ | Ymax | it is an image forming apparatus according to claim.

  According to the image forming apparatus of the present invention, it is possible to suppress a decrease in image quality even if the photoconductor has a manufacturing error or an assembly error.

1 is a diagram for describing a schematic configuration of a color printer according to an embodiment of the present invention. FIG. FIG. 2 is a diagram (part 1) for describing a configuration of an optical scanning device 2010A in FIG. FIG. 3 is a diagram (No. 2) for describing a configuration of an optical scanning device 2010A in FIG. FIG. 3 is a third diagram illustrating the configuration of an optical scanning device 2010A in FIG. FIG. 3 is a diagram (part 1) for describing a configuration of an optical scanning device 2010B in FIG. 1; FIG. 3 is a second diagram for explaining the configuration of the optical scanning device 2010B in FIG. 1; FIG. 6 is a third diagram for explaining the configuration of the optical scanning device 2010B in FIG. 1; It is a figure for demonstrating the positional relationship of the optical scanning device 2010A and the optical scanning device 2010B. FIG. 9A to FIG. 9C are diagrams for explaining the LD array included in the light source in the specific example 1, respectively. It is a figure for demonstrating the shape of each optical surface of the 1st scanning lens in the specific example 1. FIG. It is a figure for demonstrating the shape of each optical surface of the 2nd scanning lens in the specific example 1. FIG. FIG. 10 is a diagram (No. 1) for describing an arrangement example of each scanning lens of the optical scanning device 2010A in Specific Example 1; FIG. 10 is a diagram (No. 2) for explaining an arrangement example of each scanning lens of the optical scanning device 2010A in the first specific example. FIG. 10 is a diagram (No. 1) for explaining an arrangement example of each scanning lens of the optical scanning device 2010B in Specific Example 1; FIG. 10 is a diagram (No. 2) for explaining an arrangement example of each scanning lens of the optical scanning device 2010B in the first specific example. It is a figure for demonstrating the numerical example in the specific example 1. FIG. It is a figure for demonstrating the relationship between the 2nd scanning lens and the light beam in the specific example 1. FIG. It is a figure for demonstrating incident angle (phi). It is a figure for demonstrating the relationship between the incident angle (phi) and image height in the specific example 1. FIG. FIGS. 20A to 20C are diagrams for explaining the influence of manufacturing errors and assembly errors of a photosensitive drum in a conventional optical scanning apparatus having an oblique incidence optical system. FIGS. 21A to 21C are diagrams for explaining the influence of the manufacturing error and the assembly error of the photosensitive drum in the case of horizontal incidence. FIGS. 22A to 22C are diagrams for explaining the effects of the manufacturing error and the assembly error of the photosensitive drum in the specific example 1, respectively. FIG. 6 is a diagram for explaining a case where the axial direction of the photosensitive drum is inclined (axially inclined) in the XY plane with respect to the Y-axis direction. FIG. 24A and FIG. 24B are diagrams for explaining the influence of the axial tilt of the photosensitive drum in FIG. 23 when the incident angle φ at the end of the effective scanning region is large. FIG. 25A and FIG. 25B are diagrams for explaining the influence of the axial inclination of the photosensitive drum in FIG. 23 when the incident angle φ at the end of the effective scanning region is small. It is a figure for demonstrating the holding bracket of a 2nd scanning lens. 10 is a diagram for explaining the shape of each optical surface of the first scanning lens in Example 2. FIG. It is a figure for demonstrating the shape of the incident optical surface of the 2nd scanning lens in the specific example 2. FIG. It is a figure for demonstrating the shape of the emission optical surface of the 2nd scanning lens in the specific example 2. FIG. It is a figure for demonstrating the numerical example in the specific example 2. FIG. FIG. 10 is a diagram for explaining a second scanning lens in specific example 2. It is a figure for demonstrating the relationship between incident angle (phi) and the image height in the specific example 2. FIG. It is a figure for demonstrating integration of the optical scanning device 2010A and the optical scanning device 2010B. FIG. 34A and FIG. 34B are diagrams for explaining a holding mirror holding mirror. It is a figure for demonstrating the relationship between incident angle (phi) and image height at the time of adjusting a scanning line curve with a folding mirror.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a color printer 2000 according to an embodiment.

  The color printer 2000 is a tandem multicolor printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow), and includes two optical scanning devices (2010A, 2010B), four Photosensitive drums (2030a, 2030b, 2030c, 2030d), four cleaning units (2031a, 2031b, 2031c, 2031d), four charging devices (2032a, 2032b, 2032c, 2032d), and four developing rollers (2033a, 2033b, 2033c, 2033d), four toner cartridges (2034a, 2034b, 2034c, 2034d), transfer belt 2040, transfer roller 2042, fixing device 2050, paper supply roller 2054, registration roller pair 2056, paper discharge low 2058, the paper feed tray 2060, a discharge tray 2070, and a like communication control unit 2080, and a printer control device 2090.

  The communication control device 2080 controls bidirectional communication with a host device (for example, a personal computer) via a network or the like.

  The printer control device 2090 includes a CPU, a ROM described in a program written in code readable by the CPU, various data used when executing the program, a RAM as a working memory, an analog data An AD conversion circuit for converting the signal into digital data. The printer control device 2090 controls each unit in response to a request from the host device and sends image information from the host device to the optical scanning device 2010A and the optical scanning device 2010B.

  The photosensitive drum 2030a, the charging device 2032a, the developing roller 2033a, the toner cartridge 2034a, and the cleaning unit 2031a are used as a set and form an image forming station (hereinafter also referred to as “K station” for convenience) that forms a black image. Configure.

  The photosensitive drum 2030b, the charging device 2032b, the developing roller 2033b, the toner cartridge 2034b, and the cleaning unit 2031b are used as a set and form an image forming station (hereinafter also referred to as “C station” for convenience) that forms a cyan image. Configure.

  The photosensitive drum 2030c, the charging device 2032c, the developing roller 2033c, the toner cartridge 2034c, and the cleaning unit 2031c are used as a set, and form an image forming station (hereinafter also referred to as “M station” for convenience) that forms a magenta image. Configure.

  The photosensitive drum 2030d, the charging device 2032d, the developing roller 2033d, the toner cartridge 2034d, and the cleaning unit 2031d are used as a set, and form an image forming station (hereinafter also referred to as “Y station” for convenience) that forms a yellow image. Configure.

  Each photosensitive drum has a photosensitive layer formed on the surface thereof. That is, the surface of each photoconductive drum is a surface to be scanned. Each photosensitive drum is rotated in the direction of the arrow in the plane of FIG. 1 by a rotation mechanism (not shown).

  Each charging device uniformly charges the surface of the corresponding photosensitive drum.

  The optical scanning device 2010A scans the surface of the charged photosensitive drum 2030a with a light beam modulated based on the black image information from the host device, and also modulates the light beam based on the cyan image information from the host device. Then, the surface of the charged photosensitive drum 2030b is scanned.

  The optical scanning device 2010B scans the surface of the charged photosensitive drum 2030c with a light beam modulated based on magenta image information from the host device, and also modulates a light beam based on yellow image information from the host device. Then, the surface of the charged photosensitive drum 2030d is scanned.

  On the surface of each photoconductive drum, the charge disappears only in the portion irradiated with light, and a latent image corresponding to the image information is formed on the surface of each photoconductive drum. The latent image formed here moves in the direction of the corresponding developing device as the photosensitive drum rotates. Details of the optical scanning device 2010A and the optical scanning device 2010B will be described later.

  As each developing roller rotates, the toner from the corresponding toner cartridge is thinly and uniformly applied to the surface thereof. Then, when the toner on the surface of each developing roller comes into contact with the surface of the corresponding photosensitive drum, the toner moves only to a portion irradiated with light on the surface and adheres to the surface. In other words, each developing roller causes toner to adhere to the latent image formed on the surface of the corresponding photosensitive drum so as to be visualized. Here, the toner-attached image (toner image) moves in the direction of the transfer belt 2040 as the photosensitive drum rotates.

  The yellow, magenta, cyan, and black toner images are sequentially transferred onto the transfer belt 2040 at a predetermined timing, and are superimposed to form a multicolor image.

  Recording paper is stored in the paper feed tray 2060. A paper feed roller 2054 is disposed in the vicinity of the paper feed tray 2060, and the paper feed roller 2054 takes out the recording paper one by one from the paper feed tray 2060 and conveys it to the registration roller pair 2056. The registration roller pair 2056 feeds the recording paper toward the gap between the transfer belt 2040 and the transfer roller 2042 at a predetermined timing. As a result, the color image on the transfer belt 2040 is transferred to the recording paper. The recording paper on which the color image is transferred is sent to the fixing device 2050.

  In the fixing device 2050, heat and pressure are applied to the recording paper, thereby fixing the toner on the recording paper. The recording paper on which the toner is fixed is sent to the paper discharge tray 2070 via the paper discharge roller 2058 and is sequentially stacked on the paper discharge tray 2070.

  Each cleaning unit removes toner (residual toner) remaining on the surface of the corresponding photosensitive drum. The surface of the photosensitive drum from which the residual toner has been removed returns to the position facing the corresponding charging device again.

  Next, the configuration of the optical scanning device 2010A will be described.

  As shown in FIG. 2 to FIG. 4 as an example, the optical scanning device 2010A includes two light sources (2200a and 2200b), two coupling lenses (2201a and 2201b), two aperture plates (2202a and 2202b), and 2 Two cylindrical lenses (2204a, 2204b), polygon mirror 2104A, first scanning lens 2105A, three folding mirrors (2106a, 2106b, 2107a), two second scanning lenses (2108a, 2108b), two dust-proof glasses (2110a, 2110b), a scanning control device (not shown), and the like. These are assembled at predetermined positions of the optical housing 2300A (not shown in FIGS. 2 and 3, see FIG. 4).

  Here, in the XYZ three-dimensional orthogonal coordinate system, the direction along the longitudinal direction of each photosensitive drum is described as the Y-axis direction, and the direction parallel to the rotation axis of the polygon mirror 2104A is described as the Z-axis direction. Therefore, the dimension in the vertical direction in the optical housing 2300A is the height, and the dimension in the direction orthogonal to both the vertical direction and the Y-axis direction is the width.

  In the following, for convenience, the direction corresponding to the main scanning direction is abbreviated as “main scanning corresponding direction”, and the direction corresponding to the sub scanning direction is abbreviated as “sub scanning corresponding direction”.

  The light source 2200a and the light source 2200b are disposed at positions separated from each other in the sub-scanning corresponding direction (here, the same as the Z-axis direction).

  The coupling lens 2201a is disposed on the optical path of a light beam emitted from the light source 2200a (hereinafter also referred to as “light beam LBa”), and makes the light beam a substantially parallel light beam.

  The coupling lens 2201b is disposed on the optical path of a light beam emitted from the light source 2200b (hereinafter also referred to as “light beam LBb”), and makes the light beam a substantially parallel light beam.

  The aperture plate 2202a has an aperture and shapes the light beam LBa via the coupling lens 2201a.

  The aperture plate 2202b has an aperture and shapes the light beam LBb via the coupling lens 2201b.

  The cylindrical lens 2204a forms an image of the light beam LBa that has passed through the opening of the aperture plate 2202a in the vicinity of the deflection reflection surface of the polygon mirror 2104A in the Z-axis direction.

  The cylindrical lens 2204b focuses the light beam LBb that has passed through the opening of the aperture plate 2202b in the vicinity of the deflection reflection surface of the polygon mirror 2104A in the Z-axis direction.

  An optical system including the coupling lens 2201a, the aperture plate 2202a, and the cylindrical lens 2204a is a pre-deflector optical system of the K station.

  An optical system including the coupling lens 2201b, the aperture plate 2202b, and the cylindrical lens 2204b is a pre-deflector optical system of the C station.

  The polygon mirror 2104A has a six-sided mirror that rotates around its axis, and each mirror serves as a deflection reflection surface.

  The light beam LBa from the cylindrical lens 2204a and the light beam LBb from the cylindrical lens 2204b are incident on the same deflecting / reflecting surface located on the + X side of the rotation center of the polygon mirror 2104A.

  The light beam LBa from the cylindrical lens 2204a and the light beam LBb from the cylindrical lens 2204b are incident on the deflecting / reflecting surface from a direction inclined with respect to a plane orthogonal to the rotation axis of the polygon mirror 2104A.

  In the following, when the light beam is incident on the deflecting / reflecting surface, it is referred to as “oblique incidence” to be incident from a direction inclined with respect to the surface orthogonal to the rotation axis of the polygon mirror and orthogonal to the rotation axis of the polygon mirror. Incident from a direction parallel to the surface to be projected is called “horizontal incidence”. The incident angle at the time of oblique incidence is referred to as “oblique incidence angle”.

  Further, the configuration including the light source set so that the light beam is obliquely incident on the polygon mirror and the pre-deflector optical system is also referred to as “obliquely incident optical system”.

  The rotation axis of the polygon mirror 2104A is inclined with respect to the vertical direction. The inclination angle is larger than the oblique incident angle, and is set to 10 ° as an example here.

  The first scanning lens 2105A is disposed on the optical path of the light beams LBa and LBb deflected by the polygon mirror 2104A.

  The folding mirror 2106a is disposed on the optical path of the light beam LBa via the first scanning lens 2105A, and folds the optical path of the light beam LBa in the −X direction.

  The folding mirror 2107a is disposed on the optical path of the light beam LBa via the folding mirror 2106a, and folds the optical path of the light beam LBa in a direction toward the photosensitive drum 2030a.

  The second scanning lens 2108a is disposed on the optical path of the light beam LBa via the folding mirror 2107a.

  Therefore, the light beam LBa deflected by the polygon mirror 2104A is irradiated onto the photosensitive drum 2030a through the first scanning lens 2105A, the folding mirror 2106a, the folding mirror 2107a, the second scanning lens 2108a, and the dust-proof glass 2110a, and a light spot is obtained. Is formed.

  The folding mirror 2106b is disposed on the optical path of the light beam LBb via the first scanning lens 2105A, and folds the optical path of the light beam LBb in a direction toward the photosensitive drum 2030b.

  The second scanning lens 2108b is disposed on the optical path of the light beam LBb via the folding mirror 2106b.

  Therefore, the light beam LBb deflected by the polygon mirror 2104A is irradiated onto the photosensitive drum 2030b through the first scanning lens 2105A, the folding mirror 2106b, the second scanning lens 2108b, and the dust-proof glass 2110b to form a light spot. .

  The light spot on the surface of each photosensitive drum moves in the longitudinal direction of the photosensitive drum as the polygon mirror 2104A rotates. The moving direction of the light spot at this time is the “main scanning direction”, and the rotation direction of the photosensitive drum is the “sub scanning direction”.

  By the way, an area in which image information is written on each photosensitive drum is called an “effective scanning area”, an “image forming area”, an “effective image area”, or the like.

  The optical system arranged on the optical path between the polygon mirror and the photosensitive drum is also called a scanning optical system.

  Here, the K scanning optical system is constituted by the first scanning lens 2105A, the two folding mirrors (2106a, 2107a), and the second scanning lens 2108a.

  The first scanning lens 2105A, the folding mirror 2106b, and the second scanning lens 2108b constitute a scanning optical system for the C station.

  That is, the first scanning lens 2105A is shared by two stations.

  Next, the configuration of the optical scanning device 2010B will be described.

  As shown in FIG. 5 to FIG. 7 as an example, the optical scanning device 2010B includes two light sources (2200c, 2200d), two coupling lenses (2201c, 2201d), two aperture plates (2202c, 2202d), 2 Two cylindrical lenses (2204c, 2204d), polygon mirror 2104B, first scanning lens 2105B, three folding mirrors (2106c, 2106d, 2107c), two second scanning lenses (2108c, 2108d), two dust-proof glasses (2110c, 2110d), a scanning control device (not shown), and the like. These are assembled at predetermined positions of the optical housing 2300B (not shown in FIGS. 5 and 6; see FIG. 7).

  The light source 2200c and the light source 2200d are arranged at positions separated from each other in the sub-scanning corresponding direction (here, the same as the Z-axis direction).

  The coupling lens 2201c is disposed on the optical path of the light beam emitted from the light source 2200c (hereinafter also referred to as “light beam LBc”), and makes the light beam a substantially parallel light beam.

  The coupling lens 2201d is disposed on the optical path of a light beam emitted from the light source 2200d (hereinafter also referred to as “light beam LBd”), and makes the light beam a substantially parallel light beam.

  The aperture plate 2202c has an aperture and shapes the light beam LBc via the coupling lens 2201c.

  The aperture plate 2202d has an aperture and shapes the light beam LBd via the coupling lens 2201d.

  The cylindrical lens 2204c forms an image of the light beam LBc that has passed through the opening of the aperture plate 2202c in the vicinity of the deflection reflection surface of the polygon mirror 2104B in the Z-axis direction.

  The cylindrical lens 2204d forms an image of the light beam LBd that has passed through the opening of the aperture plate 2202d in the vicinity of the deflection reflection surface of the polygon mirror 2104B in the Z-axis direction.

  An optical system including the coupling lens 2201c, the aperture plate 2202c, and the cylindrical lens 2204c is a pre-deflector optical system of the M station.

  An optical system including the coupling lens 2201d, the aperture plate 2202d, and the cylindrical lens 2204d is a pre-deflector optical system of the Y station.

  The polygon mirror 2104B has a hexahedral mirror that rotates about an axis parallel to the Z axis, and each mirror serves as a deflecting reflection surface.

  The light beam LBc from the cylindrical lens 2204c and the light beam LBd from the cylindrical lens 2204d are incident on the same deflecting / reflecting surface located on the + X side of the rotation center of the polygon mirror 2104B.

  The light beam LBc from the cylindrical lens 2204c and the light beam LBd from the cylindrical lens 2204d are obliquely incident on the deflecting / reflecting surface of the polygon mirror 2104B.

  The first scanning lens 2105B is disposed on the optical path of the light beam LBc and the light beam LBd deflected by the polygon mirror 2104B.

  The folding mirror 2106c is disposed on the optical path of the light beam LBc via the first scanning lens 2105B, and folds the optical path of the light beam LBc in the −X direction.

  The folding mirror 2107c is disposed on the optical path of the light beam LBc via the folding mirror 2106c, and folds the optical path of the light beam LBc in a direction toward the photosensitive drum 2030c.

  The second scanning lens 2108c is disposed on the optical path of the light beam LBc via the folding mirror 2107c.

  Therefore, the light beam LBc deflected by the polygon mirror 2104B is applied to the photosensitive drum 2030c through the first scanning lens 2105B, the folding mirror 2106c, the folding mirror 2107c, the second scanning lens 2108c, and the dust-proof glass 2110c, and a light spot is obtained. Is formed.

  The folding mirror 2106d is disposed on the optical path of the light beam LBd via the first scanning lens 2105B, and folds the optical path of the light beam LBd in a direction toward the photosensitive drum 2030d.

  The second scanning lens 2108d is disposed on the optical path of the light beam LBd via the folding mirror 2106d.

  Therefore, the light beam LBd deflected by the polygon mirror 2104B is irradiated onto the photosensitive drum 2030d through the first scanning lens 2105B, the folding mirror 2106d, the second scanning lens 2108d, and the dustproof glass 2110d, thereby forming a light spot. .

  The light spot on the surface of each photosensitive drum moves in the longitudinal direction of the photosensitive drum as the polygon mirror 2104B rotates. The moving direction of the light spot at this time is the “main scanning direction”, and the rotation direction of the photosensitive drum is the “sub scanning direction”.

  The first scanning lens 2105B, the two folding mirrors (2106c, 2107c), and the second scanning lens 2108c constitute a scanning optical system for the M station.

  The first scanning lens 2105B, the folding mirror 2106d, and the second scanning lens 2108d constitute a Y-station scanning optical system.

  That is, the first scanning lens 2105B is shared by the two stations.

  The positional relationship between the optical scanning device 2010A and the optical scanning device 2010B is shown in FIG. 8 as an example.

<< Specific Example 1 >>
Next, a specific example 1 of main optical members in each optical scanning device will be described.

  Each light source includes an LD (Laser Diode) array having two light emitting portions with an oscillation wavelength of 655 nm (see FIG. 9A). The distance d between the two light emitting portions is 30 μm. Further, the divergence angle of the light flux in each light emitting portion is 32 ° (full width at half maximum) in the horizontal direction and 8.5 ° (full width at half maximum) in the vertical direction when the two light emitting portions are arranged horizontally.

  Each light source can be rotated about an axis passing through its substantially center and parallel to the direction toward the polygon mirror so that the pixel density of the latent image formed on the surface of the photosensitive drum corresponds to 600 dpi, that is, The rotation is adjusted so that the beam interval (beam pitch) in the sub-scanning direction on the surface of the photosensitive drum is about 42.3 μm (see FIG. 9B). Here, the rotation is adjusted so that the line segment connecting the two light emitting portions is inclined by 63.4 ° with respect to the main scanning corresponding direction (see FIG. 9C).

  Each coupling lens is a glass lens having a focal length of 14.5 mm.

  The opening of each aperture plate has a rectangular or elliptical opening with a length of 2.84 mm in the main scanning direction and a length of 0.90 mm in the sub-scanning direction (here, the same as the Z-axis direction). It is. Each aperture plate is arranged such that the center of the aperture is located in the vicinity of the focal position of the corresponding coupling lens.

  Each cylindrical lens is a glass lens having a focal length of 87.8 mm.

  The oblique incident angles of the light beams LBa and LBc are + 2.5 °, and the oblique incident angles of the light beams LBb and LBd are −2.5 °.

  The radius of the circle inscribed in the hexagonal mirror of each polygon mirror is 13 mm.

  Each first scanning lens is a resin lens having a refractive index of 1.5272 with respect to light having a wavelength of 655 nm, and has a center (on the optical axis) thickness of 5.2 mm.

  Each of the second scanning lenses is a resin lens having a refractive index of 1.5272 with respect to light having a wavelength of 655 nm, and has a center (on the optical axis) thickness of 3.0 mm.

  The shape of each optical surface (incident optical surface, exit optical surface) of each scanning lens is expressed by the following equations (1) and (2).

In the above formulas (1) and (2), the distance from the optical axis in the main scanning correspondence direction is y, and the distance from the optical axis in the sub scanning correspondence direction is z. The paraxial radius of curvature in the “main scanning section” that is a section that includes the optical axis and is parallel to the main scanning corresponding direction is Rm (= 1 / Cm), includes the optical axis, and is orthogonal to the main scanning section. The paraxial radius of curvature in the “scan section” is Rz. A ₄ , A ₆ , A ₈ ,... Are the aspheric coefficients of the shape in the main scanning correspondence direction, and B ₁ , B ₂ , B ₃ ,.

  Specific examples of Rm, Rz and each coefficient in each first scanning lens are shown in FIG. Further, specific examples of Rm, Rz, and coefficients in each second scanning lens are shown in FIG.

  Here, each optical surface (incident optical surface, exit optical surface) of each scanning lens is a so-called special toroidal surface in which the curvature in the sub-scanning direction changes depending on the lens height in the main-scanning direction.

  Only the exit optical surface of each second scanning lens has power in the sub-scanning corresponding direction. Therefore, the exit optical surface of each second scanning lens is the optical surface having the strongest power in the sub-scanning corresponding direction.

  The lateral magnification of only the scanning optical system in each station in the sub-scanning corresponding direction is −0.89 times. The design value of the size of the light spot on the surface of each photosensitive drum is 65 μm in the main scanning direction and 75 μm in the sub-scanning direction.

  Each dustproof glass is a glass plate having a wall thickness of 1.9 mm.

Specific examples of the arrangement positions of the scanning lenses are shown in FIGS. The length of the effective scanning area is 220 mm. The position on the effective scanning area where the center of the effective scanning area is 0 with respect to the Y-axis direction is called “image height”. Here, in the effective scanning region, the image height at the end on one side is −110 mm, and the image height at the end on the other side is +110 mm. The half angle of view θ ₂ is 34.2 °. 12 to 15 are schematic diagrams developed so that the optical path is parallel to the paper surface, and the values of d1 to d3 are optical path lengths.

  The reference axis of the optical surface in the first scanning lens and the reference axis of the optical surface in the second scanning lens are parallel to each other in the sub-scanning corresponding direction (here, the same as the Z-axis direction). The reference axis of the optical surface of the second scanning lens is located at a position that is 3.38 mm away from the reference axis of the optical surface of the first scanning lens on the −Z side.

  Further, in the second scanning lens, the incident position of the light beam toward the position of the image height 0 is shifted from the position on the reference axis of the optical surface in the second scanning lens with respect to the sub-scanning corresponding direction (see FIG. 17). ).

  Here, as shown in FIG. 18 as an example, an inclination angle of a light beam incident on the photosensitive drum with respect to a normal line at the incident position is denoted as “incident angle φ”. The incident angle φ when tilted clockwise is positive, and the incident angle φ when tilted counterclockwise is negative.

  The relationship between the image height and the incident angle φ in the specific example 1 is shown in FIG. Here, the incident angle φ at the other end (image height = + 110 mm) of the effective scanning region is set to 0 °. Further, the incident angle φ at one end of the effective scanning region (image height = −110 mm) is −0.03 °, and the incident angle φ at the center of the effective scanning region (image height = 0 mm) is 0.42. °. Further, the incident angle φ is 0 ° even at a position where the image height is −105.9 mm. Thus, the absolute value of the incident angle φ at the center of the effective scanning region (here, 0.42 °) is the absolute value of the incident angle φ at both ends of the effective scanning region (here, 0.03 ° and 0). The relationship of greater than (°) is satisfied.

  When an oblique incidence optical system is used, scanning line bending occurs after deflection by a polygon mirror. This scanning line curve is closest to the reference plane (the plane including the reflection point on the deflecting reflection surface and perpendicular to the rotation axis of the polygon mirror) at the center of the effective scanning area, and the reference plane becomes closer to the end of the effective scanning area. It becomes a shape that leaves. Therefore, in the conventional optical scanning apparatus having an optical system in which the scanning line curvature is corrected by the optical design, the incident angle φ of the light beam to the photosensitive drum varies depending on the image height, and the end of the effective scanning area Since it is away from the reference plane, it is incident at a tight angle from the center of the effective scanning area. That is, in the conventional optical scanning device using the oblique incidence optical system, the absolute value of the incident angle φ at the center of the effective scanning region is smaller than the absolute value of the incident angle φ at both ends of the effective scanning region.

  By the way, in a conventional optical scanning device having an oblique incidence optical system, as shown in FIG. 20A to FIG. 20C as an example, it is viewed from the Y-axis direction due to manufacturing errors and assembly errors of the photosensitive drum. If the position of the photosensitive drum surface at this time is displaced with respect to the designed position, the incident angle φ of the light beam on the photosensitive drum varies depending on the image height, so that scanning line bending occurs. The magnitude of the scanning line curve differs depending on the magnitude of the displacement.

  Here, for the sake of easy understanding, the difference between the incident position of the light beam at the center of the effective scanning region and the incident position of the light beam at one end of the effective scanning region in the sub-scanning direction is the magnitude of the scanning line bending. .

  In the case of horizontal incidence, the incident angle φ of the light beam on the photosensitive drum does not change depending on the image height, so the incident position of the light beam on the photosensitive drum when viewed from the Y-axis direction is relative to the designed incident position. Even if they are different from each other, the scanning line bending does not occur (see FIGS. 21A to 21C).

  22A to 22C show the surface of the photosensitive drum as viewed from the Y-axis direction due to manufacturing errors or assembly errors of the photosensitive drum when the optical scanning device of this embodiment is used. The scanning line bending when the position is displaced with respect to the designed position is shown. Compared with the case where the conventional optical scanning device is used, even if the angle between the light beam incident on the position where the image height is 0 mm and the light beam incident on the position where the image height is −110 mm is the same, the scanning line is bent. Is smaller than when the conventional optical scanning device is used. This is because the absolute value of the incident angle φ of the light beam incident on the position where the image height is 0 mm is made larger than the absolute value of the incident angle φ of the light beam incident on the position where the image height is −110 mm.

  Further, as an example, as shown in FIG. 23, the case where the axial direction of the photosensitive drum is assembled with the Y-axis direction inclined will be described.

  At this time, when the conventional optical scanning device is used, the incident angle φ of the light beam at the end of the effective scanning region is large as shown in FIG. 24A as an example. ), The scanning line tilt occurs.

  On the other hand, when the optical scanning device of this embodiment is used, the incident angle φ of the light beam at the end of the effective scanning region is small as shown in FIG. 25A as an example. ), The scan line inclination is small.

  Further, as shown in FIG. 26 as an example, each second scanning lens is held by the holding bracket 20 by two support portions. The position of each support portion in the Y-axis direction substantially coincides with the position where the light beam traveling toward the image height where the incident angle φ is 0 ° is incident.

  The holding bracket 20 is provided with an adjustment screw whose tip is in contact with the center of the second scanning lens in the Y-axis direction. By pushing the adjusting screw with a tool (driver), the second scanning lens can be bent in the sub-scanning corresponding direction, and the scanning line bending can be adjusted. Here, the adjusting screw is fixed in a state in which the second scanning lens is bent so that the scanning line bending amount is substantially zero.

  By the way, when the scanning line curve is adjusted, the incident position of the light beam on the surface of the photosensitive drum in the sub-scanning direction also changes. However, here, since the incident position of the light beam with the incident angle φ of 0 ° in the second scanning lens and the support portion of the holding bracket 20 substantially coincide with each other in the Y-axis direction, the incident angle φ is 0 °. The incident position in the sub-scanning direction of the light beam does not change at the image height. In this case, even if the incident position in the sub-scanning direction of the light beam on the surface of the photosensitive drum is adjusted, the change in the scanning line bending due to the manufacturing error or assembly error of the photosensitive drum can be reduced.

  Note that a mechanism (tilt adjustment mechanism) for adjusting the scan line tilt may be added to the holding bracket 20. For example, as the tilt adjustment mechanism, with respect to the Y-axis direction, a mechanism can be used in which one side end of the holding bracket 20 is used as a fulcrum and the other end is moved up and down in the sub-scanning corresponding direction.

<< Specific Example 2 >>
Next, a specific example 2 of main optical members in each optical scanning device will be described. In addition, here, it demonstrates centering around difference with the specific example 1, and the description is simplified or abbreviate | omitted about the component same or equivalent to the specific example 1 mentioned above.

  Each light source includes an LD (Laser Diode) array having two light emitting portions having an oscillation wavelength of 780 nm.

  The oblique incident angles of the light beams LBa and LBc are + 1.46 °, and the oblique incident angles of the light beams LBb and LBd are −1.46 °.

  Each first scanning lens is a resin lens having a refractive index of 1.5240 with respect to light having a wavelength of 780 nm, and has a center (on the optical axis) thickness of 5.0 mm.

  Each second scanning lens is a resin lens having a refractive index of 1.5240 with respect to light having a wavelength of 780 nm, and has a center (on the optical axis) thickness of 3.0 mm.

  The shape of each optical surface (incident optical surface, exit optical surface) of each first scanning lens and the incident optical surface of each second scanning lens is expressed by the above equations (1) and (2).

  Specific examples (unit: mm) of Rm, Rz, and each coefficient in each first scanning lens are shown in FIG. FIG. 28 shows a specific example (unit: mm) of Rm, Rz and each coefficient on the incident optical surface of each second scanning lens.

  The shape of the exit optical surface of each second scanning lens is expressed by the following equation (3) and the above equation (2).

  FIG. 29 shows a specific example (unit: mm) of Rm, Rz and each coefficient on the exit optical surface of each second scanning lens.

  Here, each of the exit optical surfaces of the second scanning lenses is a so-called special tilt eccentric surface that has no curvature in the sub-scanning corresponding direction and whose inclination in the sub-scanning cross section changes depending on the position in the main scanning corresponding direction.

  The optical correction of the scanning line bending is performed by the special tilt eccentric surface of the second scanning lens. Further, the adjustment of the scanning line bending is performed by bending the second scanning lens in the sub-scanning corresponding direction.

  The lateral magnification of only the scanning optical system in each station in the sub-scanning corresponding direction is −0.49 times.

  A specific example of the arrangement position of the scanning lens is shown in FIG.

  Each of the second scanning lenses is shifted in the sub-scanning corresponding direction so that the incident position of the light beam toward the image height 0 position coincides with the position on the reference axis of the optical surface with respect to the sub-scanning corresponding direction. It is rotated by 1.46 ° around an axis parallel to the corresponding direction (see FIG. 31). Further, with respect to the Z-axis direction, the reference axis of the second scanning lens is at a position of −5.03 mm with respect to the reference axis of the first scanning lens (see FIG. 31).

  The relationship between the image height and the incident angle φ in the specific example 2 is shown in FIG. Here, the incident angle φ at the position where the image height is +90 mm is set to be 0 °. Further, the incident angle φ at one end (image height = −110 mm) of the effective scanning region is −0.27 °, and the incident angle φ at the other end (image height = + 110 mm) is −0. 25 °. The incident angle φ at the center of the effective scanning area (image height = 0 mm) is 0.65 °. Further, the incident angle φ is 0 ° even at the position where the image height is −91.3 mm. Thus, the absolute value of the incident angle φ at the center of the effective scanning region (here, 0.65 °) is the absolute value of the incident angle φ at both ends of the effective scanning region (here, 0.27 ° and 0). .. 25 °) is satisfied.

  As described above, the color printer 2000 according to this embodiment includes the four photosensitive drums (2030a, 2030b, 2030c, 2030d) and the two optical scanning devices (2010A, 2010B).

  Each optical scanning device includes two oblique incidence optical systems, a polygon mirror, a first scanning lens, three folding mirrors, two second scanning lenses, and the like.

  With respect to the incident angle of the light beam that scans within the effective scanning area of each photosensitive drum, the absolute value of the incident angle of the light beam that enters the central part in the Y-axis direction of the effective scanning area is related to the Y-axis direction of the effective scanning area. It is set to be larger than the absolute value of the incident angle of the light beam incident on both ends.

  In this case, even if the photosensitive drum has a manufacturing error or an assembly error, the fluctuation of the scanning line curve can be reduced.

  Also, with respect to the Y-axis direction, using coordinates where the central portion of the effective scanning region is 0, one side end portion of the effective scanning region is -Ymax, and the other side end portion is Ymax, the incident angle is 0 with respect to the Y-axis direction. The absolute value | Yp | of the incident position where the angle is ° satisfies the relationship of 0.8 × | Ymax | <| Yp | ≦ | Ymax |.

  In this case, even if the photosensitive drum has a manufacturing error or an assembly error, the fluctuation in the scanning line inclination can be reduced.

  Therefore, even if the photosensitive drum has a manufacturing error or an assembly error, it is possible to suppress a decrease in image quality.

  Further, the cost and size can be reduced without degrading the image quality.

  In the above embodiment, as shown in FIG. 33 as an example, the optical scanning device 2010A and the optical scanning device 2010B may be integrated.

  In the above-described embodiment, the case where the scanning line bending amount is adjusted to be substantially zero when the scanning line bending is adjusted by the second scanning lens has been described. The scanning line bending amount at other stations may be adjusted so as to substantially coincide with the scanning line bending amount.

  In the above-described embodiment, the case where the folding mirror is arranged at the front stage of the second scanning lens has been described. However, the present invention is not limited to this, and the folding mirror may be arranged at the rear stage of the second scanning lens. .

  In this case, instead of adjusting the scanning line curve with the second scanning lens, the scanning line curve may be adjusted with a folding mirror at the rear stage of the second scanning lens.

  As shown in FIG. 34A as an example, the folding mirror whose scanning line bending is adjusted is held by the holding bracket 25 by two support portions. As an example, as shown in FIG. 34B, the position of each support portion in the Y-axis direction substantially coincides with the position where the light beam traveling toward the image height where the incident angle φ is 0 ° is incident.

  The holding bracket 25 is provided with an adjusting screw whose tip is in contact with both ends of the folding mirror in the Y-axis direction. By pushing this adjustment screw with a tool (driver), the folding mirror can be bent in a direction orthogonal to both the main scanning corresponding direction and the sub scanning corresponding direction, and the scanning line bending can be adjusted. The adjustment screw is fixed in a state in which the folding mirror is bent so that the scanning line bending amount is substantially zero. It should be noted that the scanning line bending amount at other stations may be adjusted so as to substantially match the scanning line bending amount at the K station.

  The relationship between the image height and the incident angle φ in this case is shown in FIG. Here, the incident angle φ at the position where the image height is +82.5 mm is set to be 0 °. Further, the incident angle φ at one end (image height = −110 mm) of the effective scanning region is −0.20 °, and the incident angle φ at the other end (image height = + 110 mm) is −0. 17 °. The incident angle φ at the center of the effective scanning area (image height = 0 mm) is 0.25 °. Further, the incident angle φ is 0 ° even when the image height is -78.4 mm. Thus, the absolute value of the incident angle φ at the center of the effective scanning region (here, 0.25 °) is the absolute value of the incident angle φ at both ends of the effective scanning region (here, 0.20 ° and 0). .17 °) is satisfied.

  In the above embodiment, the case where the number of photosensitive drums is four has been described. However, the present invention is not limited to this. For example, the number of photosensitive drums may be five.

  Moreover, although the said embodiment demonstrated the case where each light source had two light emission parts, it is not limited to this. For example, instead of the LD array, a surface emitting laser array (VCSEL array) in which a plurality of surface emitting laser elements (VCSEL) are integrated may be used. In this case, since one photoconductor drum can be optically scanned with a large number of light beams at the same time, it is possible to further increase the speed of image formation.

  By the way, when the incident angle of the light beam on the photosensitive drum in the sub-scanning direction is large, a so-called “trapezoidal distortion” phenomenon in which the writing width (scanning pitch) differs between the light beams occurs (for example, Japanese Patent Laid-Open No. 2004-302062). No. publication). This trapezoidal distortion increases in proportion to the number of light beams that simultaneously optically scan one photosensitive drum. However, in the above embodiment, since the incident angles in the sub-scanning direction of the light beams incident on the photosensitive drum are all small, trapezoidal distortion can be suppressed even if a surface emitting laser array is used.

  In the above embodiment, the case of the image forming apparatus in which the toner image is transferred from the photosensitive drum to the recording paper via the transfer belt has been described. However, the present invention is not limited to this, and the toner image is directly transferred to the recording paper. An image forming apparatus may be used.

  Further, an image forming apparatus using a silver salt film as the image carrier may be used. In this case, a latent image is formed on the silver salt film by optical scanning, and this latent image can be visualized by a process equivalent to a developing process in a normal silver salt photographic process. Then, it can be transferred to a photographic paper as a transfer object by a process equivalent to a printing process in a normal silver salt photographic process. Such an image forming apparatus can be implemented as an optical plate making apparatus or an optical drawing apparatus that draws a CT scan image or the like.

  Further, an image forming apparatus using a color developing medium (positive photographic paper) that develops color by the heat energy of a beam spot as an image carrier may be used. In this case, a visible image can be directly formed on the image carrier by optical scanning.

  In the above embodiment, the case of a color printer is described as the image forming apparatus. However, the present invention is also suitable for an image forming apparatus other than a printer, for example, a copier, a facsimile, or a multifunction machine in which these are integrated.

  DESCRIPTION OF SYMBOLS 20 ... Holding bracket, 25 ... Holding bracket, 2000 ... Color printer (image forming apparatus), 2010A, 2010B ... Optical scanning device, 2030a-2030d ... Photosensitive drum (image carrier), 2104A, 2104B ... Polygon mirror ( (Optical deflector) 2105A, 2105B ... first scanning lens, 2106a-2106d ... folding mirror, 2107a, 2107c ... folding mirror, 2108a-2108d ... second scanning lens, 2200a-2200d ... light source, 2300A, 2300B ... optical housing.

Japanese Patent No. 4454186 Japanese Patent Laid-Open No. 2007-10868

Claims (10)

In an image forming apparatus comprising: a photosensitive member; and an optical scanning device that optically scans a scanning region in the photosensitive member along a first direction.
The optical scanning device includes a light source, an optical deflector that obliquely enters a light beam emitted from the light source with respect to a second direction perpendicular to the first direction, and deflects the light beam by the optical deflector. A scanning optical system for guiding the emitted light beam to the photosensitive member,
With respect to the incident angle of the light beam that scans within the scanning region, the absolute value of the incident angle of the light beam that is incident on the central portion in the first direction of the scanning region is at both ends of the scanning region in the first direction. much larger than the absolute value of the angle of incidence of the light beam incident,
With respect to the first direction, using coordinates where the central portion of the scanning region is 0, one side end portion of the scanning region is -Ymax, and the other side end portion is Ymax,
With respect to the first direction, the absolute value | Yp | of the incident position where the incident angle is 0 ° satisfies a relationship of 0.8 × | Ymax | <| Yp | ≦ | Ymax |. An image forming apparatus. In an image forming apparatus comprising: a photosensitive member; and an optical scanning device that optically scans a scanning region in the photosensitive member along a first direction.
The optical scanning device includes a light source, an optical deflector that obliquely enters a light beam emitted from the light source with respect to a second direction perpendicular to the first direction, and deflects the light beam by the optical deflector. A scanning optical system for guiding the emitted light beam to the photosensitive member,
With respect to the incident angle of the light beam that scans within the scanning region, the absolute value of the incident angle of the light beam that is incident on the central portion in the first direction of the scanning region is at both ends of the scanning region in the first direction. It is larger than the absolute value of the incident angle of the incident light beam,
The image forming apparatus according to claim 1, wherein the incident angle is 0 ° at least one of the one end and the other end of the scanning region. With respect to the first direction, using coordinates where the central portion of the scanning region is 0, one side end portion of the scanning region is -Ymax, and the other side end portion is Ymax,
With respect to the first direction, the absolute value | Yp | of the incident position where the incident angle is 0 ° satisfies a relationship of 0.8 × | Ymax | <| Yp | ≦ | Ymax |. The image forming apparatus according to claim 2 . In an image forming apparatus comprising: a photosensitive member; and an optical scanning device that optically scans a scanning region in the photosensitive member along a first direction.
The optical scanning device includes a light source, an optical deflector that obliquely enters a light beam emitted from the light source with respect to a second direction perpendicular to the first direction, and deflects the light beam by the optical deflector. A scanning optical system for guiding the emitted light beam to the photosensitive member,
With respect to the incident angle of the light beam that scans within the scanning region, the absolute value of the incident angle of the light beam that is incident on the central portion in the first direction of the scanning region is at both ends of the scanning region in the first direction. It is larger than the absolute value of the incident angle of the incident light beam,
The scanning optical system of the optical scanning device includes a scanning lens having power in the second direction, and an adjustment mechanism for adjusting the scanning line bending by deforming the scanning lens,
The adjusting mechanism, the in scanning lens, the incident angle is 0 ° and made incident position images forming device light beams you characterized in that the fulcrum of the adjustment of the position of incidence towards the. With respect to the first direction, using coordinates where the central portion of the scanning region is 0, one side end portion of the scanning region is -Ymax, and the other side end portion is Ymax,
With respect to the first direction, the absolute value | Yp | of the incident position where the incident angle is 0 ° satisfies a relationship of 0.8 × | Ymax | <| Yp | ≦ | Ymax |. The image forming apparatus according to claim 4. 6. The image forming apparatus according to claim 4, wherein the incident angle is 0 ° at least one of the one end and the other end of the scanning region. In an image forming apparatus comprising: a photosensitive member; and an optical scanning device that optically scans a scanning region in the photosensitive member along a first direction.
The optical scanning device includes a light source, an optical deflector that obliquely enters a light beam emitted from the light source with respect to a second direction perpendicular to the first direction, and deflects the light beam by the optical deflector. A scanning optical system for guiding the emitted light beam to the photosensitive member,
With respect to the incident angle of the light beam that scans within the scanning region, the absolute value of the incident angle of the light beam that is incident on the central portion in the first direction of the scanning region is at both ends of the scanning region in the first direction. It is larger than the absolute value of the incident angle of the incident light beam,
The scanning optical system of the optical scanning device includes a folding mirror for folding the optical path of the light beam deflected by the optical deflector, and an adjustment mechanism for adjusting the scanning line bending by deforming the folding mirror,
The adjusting mechanism, the at folding mirror, the incident angle is 0 ° and the light beam directed to the incident position is a fulcrum of said adjusting the position of incident images formed instrumentation you wherein comprising With respect to the first direction, using coordinates where the central portion of the scanning region is 0, one side end portion of the scanning region is -Ymax, and the other side end portion is Ymax,
With respect to the first direction, the absolute value | Yp | of the incident position where the incident angle is 0 ° satisfies a relationship of 0.8 × | Ymax | <| Yp | ≦ | Ymax |. The image forming apparatus according to claim 7. 9. The image forming apparatus according to claim 7, wherein the incident angle is 0 ° at least one of the one end and the other end of the scanning region . Said light source, an image forming apparatus according to any one of claims 1 to 9, characterized in that it has a plurality of light emitting portions.

Images